In the following patent applications all filed Jun. 15, 2005 of the present applicant are disclosed and claimed techniques for monitoring single mode fibers for intrusion:
Application Ser. No. 11/152,679 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON SINGLE MODE OPTICAL FIBER USING FRESNEL REFLECTIONS.
Application Ser. No. 11/152,772 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON SINGLE MODE OPTICAL FIBER USING A STORAGE REGISTER FOR DATA.
Application Ser. No. 11/152,680 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON SINGLE MODE OPTICAL FIBER USING A SIMPLIFIED POLARIMETER.
Application Ser. No. 11/152,663 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON SINGLE MODE OPTICAL FIBER USING A COST REDUCED POLARIMETER.
Application Ser. No. 11/152,681 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON SINGLE MODE OPTICAL FIBER USING A POLARIMETER.
In the following patent applications both filed May 26, 2005 of the present applicant are disclosed and claimed techniques for monitoring multi-mode fibers for intrusion:
Application Ser. No. 11/137,776 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON AN OPTICAL FIBER USING A TRANSLATOR OF TRANSMITTED DATA FOR OPTIMUM MONITORING CONDITIONS.
Application Ser. No. 11/137,777 entitled AN INTRUSION DETECTION SYSTEM FOR USE ON MULTI-MODE OPTICAL FIBER USING AN OFFSET LAUNCH AND TAP COUPLER.
The disclosures of all of the above applications are incorporated herein by reference.
Often in data collection and analysis, for example of the type disclosed above, there arises a need to reject ambient signals in the interest of increasing functional sensitivity to the signals being detected. In the physical layer fiber optic intrusion detection systems described above, a system must detect motion in a fiber representative of an intrusion attempt, while ignoring such signals as air currents and vibrations. Simple threshold detection can otherwise be overwhelmed by the ambient.
Ambient signals are often periodic in nature, partly due to the resonant frequency of the system being monitored, fundamental to both the material and installation. For example, a fiber strung over an air duct will resonate at a repeatable frequency. A fiber in a conduit adjacent to an elevator will also have a unique frequency, while an intrusion into a fiber will often be less periodic. It is useful to desensitize the system from the ambient, while maintaining sensitivity to non-learned conditions.